Question

An array of all numbers below 100,000 with a factor of 19. Tested, working.

S= Array.new
S[0]= 19
i= 0
while S[i]+19 < 100000 do
     i+=1
     S[i] = S[i-1]+19
 end

The problem: Trying to find all numbers in the array that have a ‘reflection’ that is also in the array.

My attempt:

reflectionArray= Array.new
i=0

S.each do |s|
    reverse= s.to_s().reverse!
    S.each do |r|
    if (reverse == r)
        reflectionArray[i]= s
        i+=1
    end
  end
end

I’m expecting an array with all the mirrored factors of 19, but I get an error.
New to Ruby today, but I could’ve sworn this would work!

Answer 1

Your problem is on this line

reverse= s.to_s().reverse.to_i # No need for ! and you need to convert back to a number

But you might want to do it this way instead

s = Array.new # capital variables are for class names and constantes. Btw: actually classes also are constantes
s << 19 # you don't need to use indexes at all
while s.last +19 < 100000 do
  s << s.last + 19
end

But you could use a range to generate your array

s = (19..100000).step(19)

And to find all the reflections in the array you could simply do

reverse_array = s.select {|num| num.to_s == num.to_s.reverse }

So at the end you can do all of that in one line 🙂

(19..100000).step(19).select {|num| num.to_s == num.to_s.reverse }